GLTFSceneImporter.cs

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using System;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Text.RegularExpressions;
using GLTF;
using GLTF.Schema;
using UnityEngine;
using UnityEngine.Networking;
using UnityEngine.Rendering;
using UnityGLTF.Cache;
using UnityGLTF.Extensions;

namespace UnityGLTF
{
    public class GLTFSceneImporter
    {
        public enum MaterialType
        {
            PbrMetallicRoughness,
            KHR_materials_pbrSpecularGlossiness,
            CommonConstant,
            CommonPhong,
            CommonBlinn,
            CommonLambert
        }

        private enum LoadType
        {
            Uri,
            Stream
        }

        protected struct GLBStream
        {
            public Stream Stream;
            public long StartPosition;
        }

        protected GameObject _lastLoadedScene;
        protected readonly Transform _sceneParent;
        protected readonly Dictionary<MaterialType, Shader> _shaderCache = new Dictionary<MaterialType, Shader>();
        public int MaximumLod = 300;
        protected readonly GLTF.Schema.Material DefaultMaterial = new GLTF.Schema.Material();
        protected string _gltfUrl;
        protected string _gltfDirectoryPath;
        protected GLBStream _gltfStream;
        protected GLTFRoot _root;
        protected AssetCache _assetCache;
        protected AsyncAction _asyncAction;
        protected bool _addColliders = false;
        private LoadType _loadType;

        public GLTFSceneImporter(string gltfUrl, Transform parent = null, bool addColliders = false)
        {
            _gltfUrl = gltfUrl;
            _gltfDirectoryPath = AbsoluteUriPath(gltfUrl);
            _sceneParent = parent;
            _asyncAction = new AsyncAction();
            _loadType = LoadType.Uri;
            _addColliders = addColliders;
        }

        public GLTFSceneImporter(string rootPath, Stream stream, Transform parent = null, bool addColliders = false)
        {
            _gltfUrl = rootPath;
            _gltfDirectoryPath = AbsoluteFilePath(rootPath);
            _gltfStream = new GLBStream { Stream = stream, StartPosition = stream.Position };
            _sceneParent = parent;
            _asyncAction = new AsyncAction();
            _loadType = LoadType.Stream;
            _addColliders = addColliders;
        }

        public GameObject LastLoadedScene
        {
            get { return _lastLoadedScene; }
        }

        public virtual void SetShaderForMaterialType(MaterialType type, Shader shader)
        {
            _shaderCache.Add(type, shader);
        }

        public IEnumerator Load(int sceneIndex = -1, bool isMultithreaded = false)
        {
            if (_loadType == LoadType.Uri)
            {
                var www = UnityWebRequest.Get(_gltfUrl);

#if UNITY_2017_2_OR_NEWER
                yield return www.SendWebRequest();
#else
                yield return www.Send();
#endif

                if (www.responseCode >= 400 || www.responseCode == 0)
                {
                    throw new WebRequestException(www);
                }

                byte[] gltfData = www.downloadHandler.data;
                _gltfStream.Stream = new MemoryStream(gltfData, 0, gltfData.Length, false, true);
            }
            else if (_loadType == LoadType.Stream)
            {
                // Do nothing, since the stream was passed in via the constructor.
            }
            else
            {
                throw new Exception("Invalid load type specified: " + _loadType);
            }

            _root = GLTFParser.ParseJson(_gltfStream.Stream, _gltfStream.StartPosition);
            yield return ImportScene(sceneIndex, isMultithreaded);
        }

        protected IEnumerator ImportScene(int sceneIndex = -1, bool isMultithreaded = false)
        {
            Scene scene;
            if (sceneIndex >= 0 && sceneIndex < _root.Scenes.Count)
            {
                scene = _root.Scenes[sceneIndex];
            }
            else
            {
                scene = _root.GetDefaultScene();
            }

            if (scene == null)
            {
                throw new Exception("No default scene in gltf file.");
            }

            _assetCache = new AssetCache(
                _root.Images != null ? _root.Images.Count : 0,
                _root.Textures != null ? _root.Textures.Count : 0,
                _root.Materials != null ? _root.Materials.Count : 0,
                _root.Buffers != null ? _root.Buffers.Count : 0,
                _root.Meshes != null ? _root.Meshes.Count : 0
            );

            if (_lastLoadedScene == null)
            {
                if (_root.Buffers != null)
                {
                    // todo add fuzzing to verify that buffers are before uri
                    for (int i = 0; i < _root.Buffers.Count; ++i)
                    {
                        GLTF.Schema.Buffer buffer = _root.Buffers[i];
                        if (buffer.Uri != null)
                        {
                            yield return LoadBuffer(_gltfDirectoryPath, buffer, i);
                        }
                        else //null buffer uri indicates GLB buffer loading
                        {
                            GLTFParser.SeekToBinaryChunk(_gltfStream.Stream, i, _gltfStream.StartPosition);
                            _assetCache.BufferCache[i] = new BufferCacheData()
                            {
                                ChunkOffset = _gltfStream.Stream.Position,
                                Stream = _gltfStream.Stream
                            };
                        }
                    }
                }

                if (_root.Images != null)
                {
                    for (int i = 0; i < _root.Images.Count; ++i)
                    {
                        Image image = _root.Images[i];
                        yield return LoadImage(_gltfDirectoryPath, image, i);
                    }
                }

                // generate these in advance instead of as-needed
                if (isMultithreaded)
                {
                    yield return _asyncAction.RunOnWorkerThread(() => BuildAttributesForMeshes());
                }
            }

            var sceneObj = CreateScene(scene);

            if (_sceneParent != null)
            {
                sceneObj.transform.SetParent(_sceneParent, false);
            }

            _lastLoadedScene = sceneObj;
        }

        protected virtual void BuildAttributesForMeshes()
        {
            for (int i = 0; i < _root.Meshes.Count; ++i)
            {
                GLTF.Schema.Mesh mesh = _root.Meshes[i];
                if (_assetCache.MeshCache[i] == null)
                {
                    _assetCache.MeshCache[i] = new MeshCacheData[mesh.Primitives.Count];
                }

                for (int j = 0; j < mesh.Primitives.Count; ++j)
                {
                    _assetCache.MeshCache[i][j] = new MeshCacheData();
                    var primitive = mesh.Primitives[j];
                    BuildMeshAttributes(primitive, i, j);
                }
            }
        }

        protected virtual void BuildMeshAttributes(MeshPrimitive primitive, int meshID, int primitiveIndex)
        {
            if (_assetCache.MeshCache[meshID][primitiveIndex].MeshAttributes.Count == 0)
            {
                Dictionary<string, AttributeAccessor> attributeAccessors = new Dictionary<string, AttributeAccessor>(primitive.Attributes.Count + 1);
                foreach (var attributePair in primitive.Attributes)
                {
                    BufferCacheData bufferCacheData = _assetCache.BufferCache[attributePair.Value.Value.BufferView.Value.Buffer.Id];
                    AttributeAccessor AttributeAccessor = new AttributeAccessor()
                    {
                        AccessorId = attributePair.Value,
                        Stream = bufferCacheData.Stream,
                        Offset = bufferCacheData.ChunkOffset
                    };

                    attributeAccessors[attributePair.Key] = AttributeAccessor;
                }

                if (primitive.Indices != null)
                {
                    BufferCacheData bufferCacheData = _assetCache.BufferCache[primitive.Indices.Value.BufferView.Value.Buffer.Id];
                    AttributeAccessor indexBuilder = new AttributeAccessor()
                    {
                        AccessorId = primitive.Indices,
                        Stream = bufferCacheData.Stream,
                        Offset = bufferCacheData.ChunkOffset
                    };

                    attributeAccessors[SemanticProperties.INDICES] = indexBuilder;
                }

                GLTFHelpers.BuildMeshAttributes(ref attributeAccessors);
                TransformAttributes(ref attributeAccessors);
                _assetCache.MeshCache[meshID][primitiveIndex].MeshAttributes = attributeAccessors;
            }
        }

        protected void TransformAttributes(ref Dictionary<string, AttributeAccessor> attributeAccessors)
        {
            // Flip vectors and triangles to the Unity coordinate system.
            if (attributeAccessors.ContainsKey(SemanticProperties.POSITION))
            {
                AttributeAccessor attributeAccessor = attributeAccessors[SemanticProperties.POSITION];
                SchemaExtensions.ConvertVector3CoordinateSpace(ref attributeAccessor, SchemaExtensions.CoordinateSpaceConversionScale);
            }
            if (attributeAccessors.ContainsKey(SemanticProperties.INDICES))
            {
                AttributeAccessor attributeAccessor = attributeAccessors[SemanticProperties.INDICES];
                SchemaExtensions.FlipFaces(ref attributeAccessor);
            }
            if (attributeAccessors.ContainsKey(SemanticProperties.NORMAL))
            {
                AttributeAccessor attributeAccessor = attributeAccessors[SemanticProperties.NORMAL];
                SchemaExtensions.ConvertVector3CoordinateSpace(ref attributeAccessor, SchemaExtensions.CoordinateSpaceConversionScale);
            }
            // TexCoord goes from 0 to 3 to match GLTFHelpers.BuildMeshAttributes
            for (int i = 0; i < 4; i++)
            {
                if (attributeAccessors.ContainsKey(SemanticProperties.TexCoord(i)))
                {
                    AttributeAccessor attributeAccessor = attributeAccessors[SemanticProperties.TexCoord(i)];
                    SchemaExtensions.FlipTexCoordArrayV(ref attributeAccessor);
                }

            }
            if (attributeAccessors.ContainsKey(SemanticProperties.TANGENT))
            {
                AttributeAccessor attributeAccessor = attributeAccessors[SemanticProperties.TANGENT];
                SchemaExtensions.ConvertVector4CoordinateSpace(ref attributeAccessor, SchemaExtensions.TangentSpaceConversionScale);
            }
        }

        protected virtual GameObject CreateScene(Scene scene)
        {
            var sceneObj = new GameObject(scene.Name ?? "GLTFScene");

            foreach (var node in scene.Nodes)
            {
                var nodeObj = CreateNode(node.Value);
                nodeObj.transform.SetParent(sceneObj.transform, false);
            }

            return sceneObj;
        }

        protected virtual GameObject CreateNode(Node node)
        {
            var nodeObj = new GameObject(node.Name ?? "GLTFNode");

            Vector3 position;
            Quaternion rotation;
            Vector3 scale;
            node.GetUnityTRSProperties(out position, out rotation, out scale);
            nodeObj.transform.localPosition = position;
            nodeObj.transform.localRotation = rotation;
            nodeObj.transform.localScale = scale;

            // TODO: Add support for skin/morph targets
            if (node.Mesh != null)
            {
                CreateMeshObject(node.Mesh.Value, nodeObj.transform, node.Mesh.Id);
            }

            /* TODO: implement camera (probably a flag to disable for VR as well)
            if (camera != null)
            {
                GameObject cameraObj = camera.Value.Create();
                cameraObj.transform.parent = nodeObj.transform;
            }
            */

            if (node.Children != null)
            {
                foreach (var child in node.Children)
                {
                    var childObj = CreateNode(child.Value);
                    childObj.transform.SetParent(nodeObj.transform, false);
                }
            }

            return nodeObj;
        }

        protected virtual void CreateMeshObject(GLTF.Schema.Mesh mesh, Transform parent, int meshId)
        {
            if (_assetCache.MeshCache[meshId] == null)
            {
                _assetCache.MeshCache[meshId] = new MeshCacheData[mesh.Primitives.Count];
            }

            for (int i = 0; i < mesh.Primitives.Count; ++i)
            {
                var primitive = mesh.Primitives[i];
                var primitiveObj = CreateMeshPrimitive(primitive, meshId, i);
                primitiveObj.transform.SetParent(parent, false);
                primitiveObj.SetActive(true);
            }
        }

        protected virtual GameObject CreateMeshPrimitive(MeshPrimitive primitive, int meshID, int primitiveIndex)
        {
            var primitiveObj = new GameObject("Primitive");

            var meshFilter = primitiveObj.AddComponent<MeshFilter>();

            if (_assetCache.MeshCache[meshID][primitiveIndex] == null)
            {
                _assetCache.MeshCache[meshID][primitiveIndex] = new MeshCacheData();
            }
            if (_assetCache.MeshCache[meshID][primitiveIndex].LoadedMesh == null)
            {
                if (_assetCache.MeshCache[meshID][primitiveIndex].MeshAttributes.Count == 0)
                {
                    BuildMeshAttributes(primitive, meshID, primitiveIndex);
                }
                var meshAttributes = _assetCache.MeshCache[meshID][primitiveIndex].MeshAttributes;
                var vertexCount = primitive.Attributes[SemanticProperties.POSITION].Value.Count;

                // todo optimize: There are multiple copies being performed to turn the buffer data into mesh data. Look into reducing them
                UnityEngine.Mesh mesh = new UnityEngine.Mesh
                {
                    vertices = primitive.Attributes.ContainsKey(SemanticProperties.POSITION)
                        ? meshAttributes[SemanticProperties.POSITION].AccessorContent.AsVertices.ToUnityVector3Raw()
                        : null,
                    normals = primitive.Attributes.ContainsKey(SemanticProperties.NORMAL)
                        ? meshAttributes[SemanticProperties.NORMAL].AccessorContent.AsNormals.ToUnityVector3Raw()
                        : null,

                    uv = primitive.Attributes.ContainsKey(SemanticProperties.TexCoord(0))
                        ? meshAttributes[SemanticProperties.TexCoord(0)].AccessorContent.AsTexcoords.ToUnityVector2Raw()
                        : null,

                    uv2 = primitive.Attributes.ContainsKey(SemanticProperties.TexCoord(1))
                        ? meshAttributes[SemanticProperties.TexCoord(1)].AccessorContent.AsTexcoords.ToUnityVector2Raw()
                        : null,

                    uv3 = primitive.Attributes.ContainsKey(SemanticProperties.TexCoord(2))
                        ? meshAttributes[SemanticProperties.TexCoord(2)].AccessorContent.AsTexcoords.ToUnityVector2Raw()
                        : null,

                    uv4 = primitive.Attributes.ContainsKey(SemanticProperties.TexCoord(3))
                        ? meshAttributes[SemanticProperties.TexCoord(3)].AccessorContent.AsTexcoords.ToUnityVector2Raw()
                        : null,

                    colors = primitive.Attributes.ContainsKey(SemanticProperties.Color(0))
                        ? meshAttributes[SemanticProperties.Color(0)].AccessorContent.AsColors.ToUnityColorRaw()
                        : null,

                    triangles = primitive.Indices != null
                        ? meshAttributes[SemanticProperties.INDICES].AccessorContent.AsTriangles.ToIntArrayRaw()
                        : MeshPrimitive.GenerateTriangles(vertexCount),

                    tangents = primitive.Attributes.ContainsKey(SemanticProperties.TANGENT)
                        ? meshAttributes[SemanticProperties.TANGENT].AccessorContent.AsTangents.ToUnityVector4Raw()
                        : null
                };

                _assetCache.MeshCache[meshID][primitiveIndex].LoadedMesh = mesh;
            }

            meshFilter.sharedMesh = _assetCache.MeshCache[meshID][primitiveIndex].LoadedMesh;

            var materialWrapper = CreateMaterial(
                primitive.Material != null ? primitive.Material.Value : DefaultMaterial,
                primitive.Material != null ? primitive.Material.Id : -1
            );

            var meshRenderer = primitiveObj.AddComponent<MeshRenderer>();
            meshRenderer.material = materialWrapper.GetContents(primitive.Attributes.ContainsKey(SemanticProperties.Color(0)));

            if (_addColliders)
            {
                var meshCollider = primitiveObj.AddComponent<MeshCollider>();
                meshCollider.sharedMesh = meshFilter.mesh;
            }

            return primitiveObj;
        }

        protected virtual MaterialCacheData CreateMaterial(GLTF.Schema.Material def, int materialIndex)
        {
            MaterialCacheData materialWrapper = null;
            if (materialIndex < 0 || _assetCache.MaterialCache[materialIndex] == null)
            {
                Shader shader;

                // get the shader to use for this material
                try
                {
                    if (_root.ExtensionsUsed != null && _root.ExtensionsUsed.Contains("KHR_materials_pbrSpecularGlossiness"))
                        shader = _shaderCache[MaterialType.KHR_materials_pbrSpecularGlossiness];
                    else if (def.PbrMetallicRoughness != null)
                        shader = _shaderCache[MaterialType.PbrMetallicRoughness];
                    else if (_root.ExtensionsUsed != null && _root.ExtensionsUsed.Contains("KHR_materials_common")
                             && def.CommonConstant != null)
                        shader = _shaderCache[MaterialType.CommonConstant];
                    else
                        shader = _shaderCache[MaterialType.PbrMetallicRoughness];
                }
                catch (KeyNotFoundException)
                {
                    Debug.LogWarningFormat("No shader supplied for type of glTF material {0}, using Standard fallback", def.Name);
                    shader = Shader.Find("Standard");
                }

                shader.maximumLOD = MaximumLod;

                var material = new UnityEngine.Material(shader);

                if (def.AlphaMode == AlphaMode.MASK)
                {
                    material.SetOverrideTag("RenderType", "TransparentCutout");
                    material.SetInt("_SrcBlend", (int)UnityEngine.Rendering.BlendMode.One);
                    material.SetInt("_DstBlend", (int)UnityEngine.Rendering.BlendMode.Zero);
                    material.SetInt("_ZWrite", 1);
                    material.EnableKeyword("_ALPHATEST_ON");
                    material.DisableKeyword("_ALPHABLEND_ON");
                    material.DisableKeyword("_ALPHAPREMULTIPLY_ON");
                    material.renderQueue = (int)UnityEngine.Rendering.RenderQueue.AlphaTest;
                    material.SetFloat("_Cutoff", (float)def.AlphaCutoff);
                }
                else if (def.AlphaMode == AlphaMode.BLEND)
                {
                    material.SetOverrideTag("RenderType", "Transparent");
                    material.SetInt("_SrcBlend", (int)UnityEngine.Rendering.BlendMode.SrcAlpha);
                    material.SetInt("_DstBlend", (int)UnityEngine.Rendering.BlendMode.OneMinusSrcAlpha);
                    material.SetInt("_ZWrite", 0);
                    material.DisableKeyword("_ALPHATEST_ON");
                    material.EnableKeyword("_ALPHABLEND_ON");
                    material.DisableKeyword("_ALPHAPREMULTIPLY_ON");
                    material.renderQueue = (int)UnityEngine.Rendering.RenderQueue.Transparent;
                }
                else
                {
                    material.SetOverrideTag("RenderType", "Opaque");
                    material.SetInt("_SrcBlend", (int)UnityEngine.Rendering.BlendMode.One);
                    material.SetInt("_DstBlend", (int)UnityEngine.Rendering.BlendMode.Zero);
                    material.SetInt("_ZWrite", 1);
                    material.DisableKeyword("_ALPHATEST_ON");
                    material.DisableKeyword("_ALPHABLEND_ON");
                    material.DisableKeyword("_ALPHAPREMULTIPLY_ON");
                    material.renderQueue = -1;
                }

                if (def.DoubleSided)
                {
                    material.SetInt("_Cull", (int)CullMode.Off);
                }
                else
                {
                    material.SetInt("_Cull", (int)CullMode.Back);
                }

                if (def.PbrMetallicRoughness != null)
                {
                    var pbr = def.PbrMetallicRoughness;

                    material.SetColor("_Color", pbr.BaseColorFactor.ToUnityColorRaw());

                    if (pbr.BaseColorTexture != null)
                    {
                        var textureDef = pbr.BaseColorTexture.Index.Value;
                        material.SetTexture("_MainTex", CreateTexture(textureDef));

                        ApplyTextureTransform(pbr.BaseColorTexture, material, "_MainTex");
                    }

                    material.SetFloat("_Metallic", (float)pbr.MetallicFactor);

                    if (pbr.MetallicRoughnessTexture != null)
                    {
                        var texture = pbr.MetallicRoughnessTexture.Index.Value;
                        material.SetTexture("_MetallicRoughnessMap", CreateTexture(texture));

                        ApplyTextureTransform(pbr.MetallicRoughnessTexture, material, "_MetallicRoughnessMap");
                    }

                    material.SetFloat("_Roughness", (float)pbr.RoughnessFactor);
                }

                if (def.Extensions != null && def.Extensions.ContainsKey(KHR_materials_pbrSpecularGlossinessExtensionFactory.EXTENSION_NAME))
                {
                    KHR_materials_pbrSpecularGlossinessExtension specGloss = def.Extensions[KHR_materials_pbrSpecularGlossinessExtensionFactory.EXTENSION_NAME] as KHR_materials_pbrSpecularGlossinessExtension;

                    if (specGloss.DiffuseTexture != null)
                    {
                        var texture = specGloss.DiffuseTexture.Index.Value;
                        material.SetTexture("_MainTex", CreateTexture(texture));

                        ApplyTextureTransform(specGloss.DiffuseTexture, material, "_MainTex");
                    }
                    else
                    {
                        material.SetColor("_Color", specGloss.DiffuseFactor.ToUnityColorRaw());
                    }

                    if (specGloss.SpecularGlossinessTexture != null)
                    {
                        var texture = specGloss.SpecularGlossinessTexture.Index.Value;
                        material.SetTexture("_SpecGlossMap", CreateTexture(texture));
                        material.EnableKeyword("_SPECGLOSSMAP");

                        ApplyTextureTransform(specGloss.SpecularGlossinessTexture, material, "_SpecGlossMap");
                    }
                    else
                    {
                        material.SetVector("_SpecColor", specGloss.SpecularFactor.ToUnityVector3Raw());
                        material.SetFloat("_Glossiness", (float)specGloss.GlossinessFactor);
                    }
                }

                if (def.CommonConstant != null)
                {
                    material.SetColor("_AmbientFactor", def.CommonConstant.AmbientFactor.ToUnityColorRaw());

                    if (def.CommonConstant.LightmapTexture != null)
                    {
                        material.EnableKeyword("LIGHTMAP_ON");

                        var texture = def.CommonConstant.LightmapTexture.Index.Value;
                        material.SetTexture("_LightMap", CreateTexture(texture));
                        material.SetInt("_LightUV", def.CommonConstant.LightmapTexture.TexCoord);

                        ApplyTextureTransform(def.CommonConstant.LightmapTexture, material, "_LightMap");
                    }

                    material.SetColor("_LightFactor", def.CommonConstant.LightmapFactor.ToUnityColorRaw());
                }

                if (def.NormalTexture != null)
                {
                    var texture = def.NormalTexture.Index.Value;
                    material.SetTexture("_BumpMap", CreateTexture(texture));
                    material.SetFloat("_BumpScale", (float)def.NormalTexture.Scale);
                    material.EnableKeyword("_NORMALMAP");

                    ApplyTextureTransform(def.NormalTexture, material, "_BumpMap");
                }

                if (def.OcclusionTexture != null)
                {
                    var texture = def.OcclusionTexture.Index;

                    material.SetFloat("_OcclusionStrength", (float)def.OcclusionTexture.Strength);

                    if (def.PbrMetallicRoughness != null
                        && def.PbrMetallicRoughness.MetallicRoughnessTexture != null
                        && def.PbrMetallicRoughness.MetallicRoughnessTexture.Index.Id == texture.Id)
                    {
                        material.EnableKeyword("OCC_METAL_ROUGH_ON");
                    }
                    else
                    {
                        material.SetTexture("_OcclusionMap", CreateTexture(texture.Value));

                        ApplyTextureTransform(def.OcclusionTexture, material, "_OcclusionMap");
                    }
                }

                if (def.EmissiveTexture != null)
                {
                    var texture = def.EmissiveTexture.Index.Value;
                    material.EnableKeyword("EMISSION_MAP_ON");
                    material.EnableKeyword("_EMISSION");
                    material.SetTexture("_EmissionMap", CreateTexture(texture));
                    material.SetInt("_EmissionUV", def.EmissiveTexture.TexCoord);

                    ApplyTextureTransform(def.EmissiveTexture, material, "_EmissionMap");
                }

                material.SetColor("_EmissionColor", def.EmissiveFactor.ToUnityColorRaw());

                materialWrapper = new MaterialCacheData
                {
                    UnityMaterial = material,
                    UnityMaterialWithVertexColor = new UnityEngine.Material(material),
                    GLTFMaterial = def
                };

                materialWrapper.UnityMaterialWithVertexColor.EnableKeyword("VERTEX_COLOR_ON");

                if (materialIndex > 0)
                {
                    _assetCache.MaterialCache[materialIndex] = materialWrapper;
                }
            }

            return materialIndex > 0 ? _assetCache.MaterialCache[materialIndex] : materialWrapper;
        }

        protected virtual UnityEngine.Texture CreateTexture(GLTF.Schema.Texture texture)
        {
            if (_assetCache.TextureCache[texture.Source.Id] == null)
            {
                var source = _assetCache.ImageCache[texture.Source.Id];
                var desiredFilterMode = FilterMode.Bilinear;
                var desiredWrapMode = UnityEngine.TextureWrapMode.Repeat;

                if (texture.Sampler != null)
                {
                    var sampler = texture.Sampler.Value;
                    switch (sampler.MinFilter)
                    {
                        case MinFilterMode.Nearest:
                            desiredFilterMode = FilterMode.Point;
                            break;
                        case MinFilterMode.Linear:
                        default:
                            desiredFilterMode = FilterMode.Bilinear;
                            break;
                    }

                    switch (sampler.WrapS)
                    {
                        case GLTF.Schema.WrapMode.ClampToEdge:
                            desiredWrapMode = UnityEngine.TextureWrapMode.Clamp;
                            break;
                        case GLTF.Schema.WrapMode.Repeat:
                        default:
                            desiredWrapMode = UnityEngine.TextureWrapMode.Repeat;
                            break;
                    }
                }

                if (source.filterMode == desiredFilterMode && source.wrapMode == desiredWrapMode)
                {
                    _assetCache.TextureCache[texture.Source.Id] = source;
                }
                else
                {
                    var unityTexture = UnityEngine.Object.Instantiate(source);
                    unityTexture.filterMode = desiredFilterMode;
                    unityTexture.wrapMode = desiredWrapMode;
                    _assetCache.TextureCache[texture.Source.Id] = unityTexture;
                }
            }

            return _assetCache.TextureCache[texture.Source.Id];
        }

        protected virtual void ApplyTextureTransform(TextureInfo def, UnityEngine.Material mat, string texName)
        {
            IExtension extension;
            if (_root.ExtensionsUsed != null &&
                _root.ExtensionsUsed.Contains(ExtTextureTransformExtensionFactory.EXTENSION_NAME) &&
                def.Extensions != null &&
                def.Extensions.TryGetValue(ExtTextureTransformExtensionFactory.EXTENSION_NAME, out extension))
            {
                ExtTextureTransformExtension ext = (ExtTextureTransformExtension)extension;

                Vector2 temp = ext.Offset.ToUnityVector2Raw();
                temp = new Vector2(temp.x, -temp.y);
                mat.SetTextureOffset(texName, temp);

                mat.SetTextureScale(texName, ext.Scale.ToUnityVector2Raw());
            }
        }

        protected const string Base64StringInitializer = "^data:[a-z-]+/[a-z-]+;base64,";

        protected virtual IEnumerator LoadImage(string rootPath, Image image, int imageID)
        {
            if (_assetCache.ImageCache[imageID] == null)
            {
                Texture2D texture = null;
                if (image.Uri != null)
                {
                    var uri = image.Uri;

                    Regex regex = new Regex(Base64StringInitializer);
                    Match match = regex.Match(uri);
                    if (match.Success)
                    {
                        var base64Data = uri.Substring(match.Length);
                        var textureData = Convert.FromBase64String(base64Data);
                        texture = new Texture2D(0, 0);
                        texture.LoadImage(textureData);
                    }
                    else if (_loadType == LoadType.Uri)
                    {
                        var www = UnityWebRequest.Get(Path.Combine(rootPath, uri));
                        www.downloadHandler = new DownloadHandlerTexture();

#if UNITY_2017_2_OR_NEWER
                        yield return www.SendWebRequest();
#else
                        yield return www.Send();
#endif

                        // HACK to enable mipmaps :(
                        var tempTexture = DownloadHandlerTexture.GetContent(www);
                        if (tempTexture != null)
                        {
                            texture = new Texture2D(tempTexture.width, tempTexture.height, tempTexture.format, true);
                            texture.SetPixels(tempTexture.GetPixels());
                            texture.Apply(true);
                        }
                        else
                        {
                            Debug.LogFormat("{0} {1}", www.responseCode, www.url);
                            texture = new Texture2D(16, 16);
                        }
                    }
                    else if (_loadType == LoadType.Stream)
                    {
                        var pathToLoad = Path.Combine(rootPath, uri);
                        var file = File.OpenRead(pathToLoad);
                        byte[] bufferData = new byte[file.Length];
                        file.Read(bufferData, 0, (int)file.Length);
#if !WINDOWS_UWP
                        file.Close();
#else
                        file.Dispose();
#endif
                        texture = new Texture2D(0, 0);
                        texture.LoadImage(bufferData);
                    }
                }
                else
                {
                    texture = new Texture2D(0, 0);
                    var bufferView = image.BufferView.Value;
                    var data = new byte[bufferView.ByteLength];

                    var bufferContents = _assetCache.BufferCache[bufferView.Buffer.Id];
                    bufferContents.Stream.Position = bufferView.ByteOffset + bufferContents.ChunkOffset;
                    bufferContents.Stream.Read(data, 0, data.Length);
                    texture.LoadImage(data);
                }

                _assetCache.ImageCache[imageID] = texture;
            }
        }

        protected virtual IEnumerator LoadBuffer(string sourceUri, GLTF.Schema.Buffer buffer, int bufferIndex)
        {
            if (buffer.Uri != null)
            {
                Stream bufferStream = null;
                var uri = buffer.Uri;

                Regex regex = new Regex(Base64StringInitializer);
                Match match = regex.Match(uri);
                if (match.Success)
                {
                    string base64String = uri.Substring(match.Length);
                    byte[] base64ByteData = Convert.FromBase64String(base64String);
                    bufferStream = new MemoryStream(base64ByteData, 0, base64ByteData.Length, false, true);
                }
                else if (_loadType == LoadType.Uri)
                {
                    var www = UnityWebRequest.Get(Path.Combine(sourceUri, uri));

#if UNITY_2017_2_OR_NEWER
                    yield return www.SendWebRequest();
#else
                    yield return www.Send();
#endif

                    bufferStream = new MemoryStream(www.downloadHandler.data, 0, www.downloadHandler.data.Length, false, true);
                }
                else if (_loadType == LoadType.Stream)
                {
                    var pathToLoad = Path.Combine(sourceUri, uri);
                    bufferStream = File.OpenRead(pathToLoad);
                }

                _assetCache.BufferCache[bufferIndex] = new BufferCacheData()
                {
                    Stream = bufferStream
                };
            }
        }

        protected static string AbsoluteUriPath(string gltfPath)
        {
            var uri = new Uri(gltfPath);
            var partialPath = uri.AbsoluteUri.Remove(uri.AbsoluteUri.Length - uri.Query.Length - uri.Segments[uri.Segments.Length - 1].Length);
            return partialPath;
        }

        protected static string AbsoluteFilePath(string gltfPath)
        {
            var fileName = Path.GetFileName(gltfPath);
            var lastIndex = gltfPath.IndexOf(fileName);
            var partialPath = gltfPath.Substring(0, lastIndex);
            return partialPath;
        }
    }
}